Ultrasonic sensor for testing U-shaped tubes of a heat exchanger

ABSTRACT

An ultrasonic sensor for testing tubes of a heat exchanger having a U-shaped tube bundle includes a probe head unit having an ultrasonic vibrator and two opposite ends. Two flexible hollow shafts are each connected to a respective one of the ends of the probe head unit. One of the hollow shafts is rotatably supported in a guide tip and the other of the hollow shafts is rotatably supported in a cylindrical sheath. An electric drive unit is connected to and fixed against torque relative to the other hollow shaft. The flexible hollow shafts have supports at predetermined axial intervals. A sealing body is connected to the cylindrical sheath for sealing off a flow of a fluid for coupling the ultrasonic vibrator and a pusher hose is also connected to the cylindrical sheath.

The invention relates to an ultrasonic sensor for testing tubes of aheat exchanger having a U-shaped tube bundle or nest, such as are used,for example, in steam generators in nuclear power plants.

Published European application No. 0 086 341 discloses an ultrasonicsensor for non-destructive testing of cylindrical hollow spaces, whichis provided with a rotating probe head that is rotatably supported atone end in a guide and at the other in a cylindrical, rigid sheath. Theprobe head includes a holder body containing an ultrasonic vibratordisposed in a radially extending bore, that is, transversely to thelongitudinal axis of the sensor. That ultrasonic vibrator is disposed inthe bore in such a way that it is displaceable in the radial directionand is firmly clamped with a screw. A coupling fluid is supplied to theultrasonic vibrator through a hose guided by the sensor. An electricmotor with a step-down gear that is accommodated inside the rigidcylindrical sheath of the sensor is used to drive the rotating probehead. Adjoining the sheath is a guide portion having a sealing body, towhich a pusher hose is secured. A pusher apparatus with which the sensoris thrust into the tube of the heat exchanger to be tested, isassociated with the pusher hose.

Such a prior art ultrasonic sensor can only be used for testing straightportions of the tubes of the tube bundle of a heat exchanger. It is notpossible to feed the ultrasonic sensor into the curved portion of thetubes of a tube bundle.

It is accordingly an object of the invention to provide an ultrasonicsensor for testing U-shaped tubes of a heat exchanger, which overcomesthe hereinafore-mentioned disadvantages of the heretofore-known devicesof this general type, which is simply constructed and with which theultrasound measurements can be made even in the curved region of aU-shaped tube.

With the foregoing and other obJects in view there is provided, inaccordance with the invention, an ultrasonic sensor for testing tubes ofa heat exchanger having a U-shaped tube bundle, comprising a probe headunit having an ultrasonic vibrator and two opposite ends, two flexiblehollow shafts each being connected to a respective one of the ends ofthe probe head unit, a guide tip in which one of the hollow shafts isrotatably supported, a cylindrical sheath in which the other of thehollow shafts is rotatably supported, an electric drive unit connectedto and fixed against torque relative to the other hollow shaft, theflexible hollow shafts having supports at predetermined axial intervals,a sealing body connected to the cylindrical sheath for sealing off aflow of a fluid for coupling the ultrasonic vibrator, and a pusher hoseconnected to the cylindrical sheath.

In this way, the drive forces that must be brought to bear for therotational motion of the probe head in the vicinity of the curve of thetube can be kept low, so an electric motor accommodated in the sensorcan be used to drive the probe head, despite the small size of themotor.

The coupling fluid emerges from the sealing body in the downstreamdirection, as seen in the insertion direction of the sensor, and fillsthe space between the inner wall surface of the tube to be tested andthe surface of the sensor, so that good sliding of the supports is alsoassured.

In accordance with another feature of the invention, there is providedanother sealing body disposed on the outer periphery of the guide tip,in addition to the sealing body disposed on the cylindrical sheath. Thisis done in order to prevent the coupling fluid from escaping during thetransition of the guide tip from the upwardly oriented position to thedownwardly oriented position in the tube curve.

In accordance with a further feature of the invention, the guide tip hasat least one outlet opening formed therein for the coupling fluid usedfor coupling the ultrasonic vibrator. This provides a furtherimprovement in the sliding characteristics of the sensor and therefore areduction in the drive forces. With this feature, the guide tip and thesupports preceding the probe head are moistened upon insertion of thesensor into the tube to be tested, so that these parts slide moreeasily.

In accordance with an added feature of the invention, the supports areslide rings.

In accordance with an additional feature of the invention, the supportsare rings, and there are provided ball bearings supporting the rings onthe flexible hollow shafts. This reduces the friction of the sensor onthe inner wall surface of the tube to a minimum, so that the drive forcefor the motor unit can be kept particularly low.

In accordance with yet another feature of the invention, there isprovided a shutoff valve upstream of the outlet opening, the shutoffvalve including means for permitting fluid flow through the outlet orfor uncovering the outlet to a tube to be tested when the guide tipassumes or enters an upwardly oriented position and for blocking fluidflow through the outlet when the guide tip assumes or enters adownwardly oriented position, by utilizing gravity. As a result, in thetransition of the guide tip from the upwardly oriented to the downwardlyinclined position, the ultrasonic vibrator coupling fluid is preventedfrom escaping from the tube to be tested.

In accordance with yet a further feature of the invention, there isprovided a holder or retaining body from which the ultrasonic vibratoris cardanically suspended. This provides good adaptation of the probehead to the curvature of the inner tube wall surface in the curvedregion.

In accordance with a concomitant feature of the invention, the flexiblehollow shafts are formed of helically wound spring wire having mutuallyinterlocking windings.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin an ultrasonic sensor for testing U-shaped tubes of a heat exchanger,it is nevertheless not intended to be limited to the details shown,since various modifications and structural changes may be made thereinwithout departing from the spirit of the invention and within the scopeand range of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

FIG. 1 is an exploded fragmentary, diagrammatic, longitudinal-sectionalview showing details of the forward portion of an ultrasonic sensor onan enlarged scale; and

FIG. 2 is an exploded partly elevational and partly sectional view ofthe entire sensor with details of the rear portion.

Referring now to the figures of the drawing in detail and first,particularly, to FIG. 2 thereof, there is seen an ultrasonic sensorhaving a probe head unit 1 that is rotationally supported at oppositeends thereof through respective hollow shafts 16 and 17. The hollowshaft 16 is in turn supported in a guide tip 2 and the hollow shaft 17is in turn supported in a drive and signal transmission unit 3. Supports14 are disposed at predetermined axial intervals along the flexiblehollow shafts 16, 17.

The drive and signal transmission unit 3 is adjoined by a guide segment4 having a sealing body 5 with discs, to which a pusher hose 6 issecured. The sensor is thrust into the tube of a heat exchanger throughthe use of the pusher hose 6. A pusher apparatus, which is known in theart, is used for this purpose.

As FIG. 1 shows in a longitudinal section, the probe head unit 1 has aholder 10 for a probe head 8 with an ultrasonic vibrator 7. The probehead is movable through bearing journals 9a, 9b, 9c, 9d in two axeswhich are at right angles to one another. In other words, the probe headis cardanically suspended. The bearing journals 9a-9d are suspended onthe holder 10 through two parallel rocking levers 11 and joints 12. Aspring 13 secured to the holder 10 acts through the rocking lever 11 topress the probe head 8 against the inner wall surface of the tube to betested.

Both ends of the holder 10 are provided with extensions 10a, 10b onwhich the supports 14, which are constructed in the form of slide rings,are secured. The extension 10a has a female thread 15, into which oneend 16a of the flexible hollow shaft 16 is screwed. The hollow shaft 16is provided with one or more of the supports 14. The other end 16b ofthe flexible hollow shaft 16 is screwed into a female thread 18a of ashaft journal 18, which is rotatably disposed in a jacket 2a of theguide tip 2 through two ball bearings 19a, 19b. The jacket 2a has acollar 2b serving as a support in the tube, and another sealing body 20which is constructed in the form of two rubber washers 20a, 20b, whichare retained by a screw cap 20c. Elastic guide tongues 21 which are benttoward an end piece 22 of the guide tip 2, are disposed on the screw cap20c. The end piece 22 is frustoconical and is screwed onto the shaftjournal 18.

On the drive side, the holder 10 the extension 10b of the probe head 8also has a female thread 15 into which an elastic hollow shaft 17 isscrewed. The hollow shaft 17 is connected through a plurality ofnon-illustrated interposed supports 14 and a hollow shaft journal 23 tothe drive and signal transmission unit unit 3, which includes astep-down gear 24 and an electric motor 25, in such a manner as to befixed against relative torque. The drive and signal transmission unit 3is disposed on a shell body 26, on which the shaft journal 23 is alsosupported, through a ball bearing 31. The shell body 26 is surrounded bya sheath 27 and is detachably connected thereto. In the direction towardthe probe head, the end of the shell body 26 has a hood 28, which isscrewed onto a thread 26a of the shell body 26. Respective ring seals30, 29 are disposed between the sheath 27 and shell body 26 and betweenthe hood 28 and shell body 26 for sealing purposes. A ball bearing 21ais anchored on the shaft journal 23 with an eye nut 31a.

Besides the hood 28, a double roller bearing 32 is also disposed on theshaft journal 23. The double roller bearing 32 has an outer bearing body33 which is provided with finger-like elastic laminations 34 forsupporting the drive unit 3 on the tube to be tested. A V-ring seal 35is also disposed between the hood 28 and the double roller bearing 32,for sealing off the interior of the drive unit from the ingress ofcoupling fluid. Various slide contacts 36 are disposed in the interiorof the drive unit, between the eye nut 31a and the ball bearing 31.These contact 36 transmit electrical ultrasonic vibrator signalstransmitted through a cable 37 to stationary connection lines 38 leadingto a plug 39 on the end of the shell body 26. Additional lines 40b, withan interposed diode, lead from the electric motor 25 to the plug 39. Theplug 39 includes a bayonet mount, for the sake of easy mechanical andelectrical disconnection of the drive unit 3 from the guide segment 4shown in FIG. 2.

A coaxial cable 42 for transmitting the electrical signals of theultrasonic vibrator is provided in the pusher hose 6 which is connectedto the guide segment 4 by means of a coupler 41 and the sealing body 5.A further cable 43 serves to supply voltage to the motor, which isoperated with direct current. Another cable 44 transmits signals fromwhich the rpm and angular position of the probe head are derived.

Also accommodated in the thrust hose 6 is a hose 45, which extends asfar as the guide segment 4 and serves to deliver fluid, such as water,used to couple the vibrator. A conduit 41a, which is provided in thecoupler and into which the hose is threaded, is provided with outletopenings 41b, so that the coupling fluid can flow to the ultrasonicvibrator 7 and as far as the rubber washers 20a, 20b of the guide tip 2,through the space defined by the inner wall surface of the tube to betested, the disks of the sealing body 5, and the sheath 27.

As FIG. 1 shows, the rotatable part of the hollow shaft 16a or the shaftjournal 18 or the holder 10 has an opening 46, leading from the outsidein, through which the coupling fluid can reach the hollow space of theshaft journal 18. A bore 47 leads from the hollow space of the shaftjournal 18 to the end piece 22 of the guide tip 2, which is providedwith outlet openings 48, 49 leading toward the angularly bentlaminations 21.

A shutoff valve 50 is disposed in the hollow space of the shaft journal18 upstream of the outlet openings and is constructed in such a way thatby utilizing gravity, the valve outlet leading to the tube to be testedis uncovered as long as the guide tip 2 of the ultrasonic sensor is inan upwardly oriented position, and the valve outlet is closed wheneverthe guide tip 2 enters a downwardly oriented position. As a result, asthe sensor is introduced into the upwardly oriented curved portion ofthe tube to be tested, the laminations 21 on the guide tip 2, which areused for guidance and are bent at an angle and the sealing rings 20a,20b are moistened with fluid, so that the sensor slides more easily. Atthe transition of the guide tip 2 from the upwardly oriented location inthe tube to the downwardly inclined location, the shutoff valve 50closes, so that the coupling fluid cannot run out of the guide tip 2.The shutoff valve 50 may simply be constructed as a ball valve with asealing seat 52, in which case whenever the guide tip 2 enters adownward inclined position, a ball 51 rests on the sealing seat 52 dueto gravity and prevents a flow of the fluid through it. In the otherposition of the guide tip, the ball 51 assumes a position in which theflow of fluid is allowed.

It is advantageous to form the hollow shafts 16 and 17 from hollow shaftlengths, and to join them together, with the supports 14 inbetween.

As shown in the enlarged portion of FIG. 1 below one of the supports 14,the flexible hollows shafts 16, 17 are preferably formed of a helicallywound spring wire 53, the windings of which interlock with one another.The windings have helical ribs 53a that form a male thread. The supports14 have annular extensions 40 on both ends, which are provided with afemale thread 40a, so that the hollow shafts or shaft segments 16, 17can be screwed into the supports and secured. The supports 14 aresuitably constructed in the form of rings, which are supported throughball bearings 55 on the flexible hollow shafts or shaft segments 16, 17.A rope or cable 54 is guided through the sensor, anchored to the guidetip 2, and used to pull the entire sensor out of the tube to be tested.At the site where the ultrasonic vibrator 7 is installed, the rope 54 iswrapped around the cardanically suspended head.

We claim:
 1. Ultrasonic sensor for testing tubes of a heat exchangerhaving a U-shaped tube bundle, comprising a probe head unit having anultrasonic vibrator and two opposite ends, two flexible hollow shaftseach being connected to a respective one of said ends of said probe headunit, a guide tip in which one of said hollow shafts is rotatablysupported, a cylindrical sheath in which the other of said hollow shaftsis rotatably supported, an electric drive unit connected to and fixedagainst torque relative to said other hollow shaft, said flexible hollowshafts having supports at predetermined axial intervals, a sealing bodyconnected to said cylindrical sheath for sealing off a flow of a fluidfor coupling said ultrasonic vibrator, a pusher hose connected to saidcylindrical sheath, another sealing body disposed on the outer peripheryof said guide tip, said guide tip having at least one outlet opening forcoupling fluid formed therein, and a shutoff valve upstream of saidoutlet opening, said shutoff valve including means for permitting fluidflow through said outlet to a tube to be tested when said guide tipassumes an upwardly oriented position and for blocking fluid flowthrough said outlet when said guide tip assumes a downwardly orientedposition, by utilizing gravity.
 2. Ultrasonic sensor according to claim1, wherein said supports are slide rings.
 3. Ultrasonic sensor accordingto claim 1, wherein said supports are rings, and including ball bearingssupporting said rings on said flexible hollow shafts.
 4. Ultrasonicsensor according to claim 1, including a holder from which saidultrasonic vibrator is cardanically suspended.
 5. Ultrasonic sensoraccording to claim 1, wherein said flexible hollow shafts are formed ofhelically wound spring wire having mutually interlocking windings.